Allow constant folding of && and ||.

frog/leg/operations.dart

Index: frog/leg/operations.dart
diff --git a/frog/leg/operations.dart b/frog/leg/operations.dart
index 0f5ea51f6da5595c823b0b0c52191e0a2d913875..8ad5427d01f1e2d320ded4f8f4d14d8bcd74c2a2 100644
--- a/frog/leg/operations.dart
+++ b/frog/leg/operations.dart
@@ -105,6 +105,31 @@ class ShiftRightOperation extends BinaryIntOperation {
   }
 }
 
+class BinaryBoolOperation implements BinaryOperation {
+  const BinaryBoolOperation();
+  Constant fold(Constant left, Constant right) {

[Lasse Reichstein Nielsen, 2012/03/27 07:48:53]

This seems like a pretty weak folding, if it requires the right-hand-side to be
constant.
Is it not possible to fold if just the LHS is constant and the short-circuiting
value?

+    if (left.isBool() && right.isBool()) {
+      BoolConstant leftBool = left;
+      BoolConstant rightBool = right;
+      bool resultValue = foldBools(leftBool.value, rightBool.value);
+      return new BoolConstant(resultValue);
+    }
+    return null;

[Lasse Reichstein Nielsen, 2012/03/27 07:48:53]

If left or right are not boolean, you can still fold, since any non-boolean is
converted to false.

+  }
+
+  abstract bool foldBools(bool left, bool right);
+}
+
+class BooleanAnd extends BinaryBoolOperation {
+  const BooleanAnd();
+  bool foldBools(bool left, bool right) => left && right;
+}
+
+class BooleanOr extends BinaryBoolOperation {
+  const BooleanOr();
+  bool foldBools(bool left, bool right) => left || right;
+}
+
 class ArithmeticNumOperation implements BinaryOperation {
   const ArithmeticNumOperation();
   Constant fold(Constant left, Constant right) {